The present invention relates to eyewear, and more particularly to earstems configured to accommodate a wide deviation from the standard Alderson head size while providing a medially directed force at the distal portion of the earstems so as to increase the retentive force between the eyewear and the head.
Although corrective lenses are specifically crafted to accommodate the unique vision defects of an individual, the frames and earstems used to retain the lenses are typically a standard size and not crafted to conform to the particular contours of the head of each individual. Lenses which are employed in filtering eyewear such as sunglasses are also typically retained in stock frames. As it is virtually impossible to mass produce stock frames which fit every individual's head, the stock frames are constructed to conform to an idealized "standard" adult head such as that known in the art as the standard Alderson head form.
In determining the dimensions of the standard adult head, statistical data reflecting the range of cranial dimensions in an adult population was compiled to provide a hypothetical size head which represents the statistical median of the normal variations in the size of the adult head. These standard dimensions are then used to size the stock frames. Typically, the Alderson head form provides the anatomical model upon which stock frames are based. Therefore, the stock frames are constructed to conform to the hypothetical "standard" head rather than specific individuals.
As a result, such frames often result in a fit which is either too tight or too loose about the head of an individual. A tight fitting frame may cause localized pain and headaches, while a loose fitting frame may allow the eyewear to fall from the head and damage the frame or the lens. This is particularly disadvantageous for protective eyewear such as sunglasses which are to be used in active sports, such as bicycle racing or skiing. Additionally, in the event that corrective lenses vary in weight between the lenses, the uneven weight distribution may create localized pressure points causing discomfort.
A variety of means have been employed to improve the securing of eyewear to the head. These devices have included modifications from the use of the traditional hook at the end of the temple bar for wrapping behind the ear to loose strings or straps which connect the temples of the eyewear around the back of the wearer's head, thereby preventing the glasses from becoming completely displaced from the body. Alternatively, an elastic strap connecting the temples has been employed to engage the wearer's head and secure the eyewear in the desired position.
The prior attempts to improve the retention of eyewear about the wearer's head have also included the use of rubber or rubber-like plastic boots applied to the free ends of the temples for increasing the friction between the eyeglasses and the head, such as shown in U.S. Pat. No. 3,684,356 to Bates. The Bates device, however, appears somewhat clumsy and, therefore, detracts from the appearance of the eyewear. In addition, the Bates device does not provide for a greater variation in the range of head widths on which the glasses can be worn. For example, a wider than median head will frequently contact the inside surface of the temple bar somewhere in between the eyeglass frame and the hook over the ear. This causes the hook portion to be lifted away from the head, thereby nullifying any advantage to such boots as the Bates device.
Another prior attempt to improve eyewear retention is disclosed in the Nelson patent (U.S. Pat. No. 2,561,402), which discloses use of fluid chambers at the interface of the free end of the temples and the head. Nelson uses the fluid chambers in an effort to evenly distribute pressure between the temple and the head. As the fluid chambers of Nelson are permanently affixed to the temple in a predetermined orientation, modification for specific individuals is unavailable. In addition, the fluid retained within the chambers adds an undesired weight to the eyewear, the device is relatively complex from a manufacturing point of view, and the durability of the device is likely not as good as solid plastic alternatives.
Notwithstanding the foregoing, there remains a need for providing a means of improving the compatibility of eyewear and the wearer so as to improve retention of the eyewear throughout a broader spectrum of head sizes within the population. A need also exists for a device which may be used in conjunction with a lens retained within a frame or alternatively, a lens alone. A further need exists for a device which may be used in cooperation with supplemental retaining devices without permanently altering the configuration of the eyewear.